I wonder might this be partly due to licensing concerns given uutils have acknowledged they've copied GNU GPL code. From their latest release notes (https://github.com/uutils/coreutils/releases/tag/0.12.0):

"Also, some contributions had carried comments and code over from GNU coreutils, against our own rule that uutils is an original implementation. We reviewed the tree and rewrote what we found, in comments and in the few functions that followed the C too closely"